Method of impregnation of food and vitamin C-containing egg and pidan-like egg obtained by this method

ABSTRACT

The method of impregnation treatment for foods comprises impregnating the foods with a liquid component or a gas component by contacting the foods with the liquid component or the gas component after vacuum treatment or in the vacuum state and/or cooling the foods in contact with the liquid component. The method of impregnation treatment for foods of the present invention enables readily impregnating various kinds of foods with various liquid components or gas components. The invention also provides a vitamin C-containing egg and a pidan-like egg.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of impregnation treatment forfoods by which foods are impregnated with a liquid component or a gascomponent.

The present invention also relates to a method for obtaining vitaminC-containing eggs by impregnating eggs with a vitamin C component, and amethod for obtaining pidan-like eggs by impregnating eggs with an alkalicomponent.

2. Description of the Prior Art

There are a variety of foods known as impregnated with seasonings or thelike. These foods are obtained by such a cooking method as boilingfoods, such as vegetables, meats and fishes, in hot water containingseasonings, or soaking the foods in seasonings.

However, boiling of foods often results in hardened or softened foodsdue to the heat and inevitably causes the foods to have a differenteating texture from that before the heating. Also, boiling of foodsrequires a long time to complete sufficient impregnation of the foodswith seasonings, and it necessitates a large amount of heat energy toconduct the heating.

To shorten the time required to flavor foods by boiling,JP-B-7(1995)/112453 proposes a flavoring method by preparation in adepressurized cooker, in which a cooker containing cooking ingredientsand seasoning components is depressurized to impregnate the ingredientswith the flavor quickly into the inside. However, this method onlyachieves, when water-rich ingredients are depressurized as being soakedin a seasoning liquid, the substitution of the moisture in theingredients with the seasoning liquid due to the difference of osmoticpressures, and remains unsatisfactory in terms of shortening of theflavoring time.

Meanwhile, soaking of foods in seasonings, although allowing foods to beimpregnated with seasonings at ordinary temperature or low temperatures,requires a further longer time to complete deep impregnation of thefoods with seasonings than by the boiling method.

In order to impregnate foods with liquids by a method other than theseconventional cooking methods, it has been proposed (inJP-A-4(1992)/287665) that beef can be injected with a liquid andmassaged to disperse the liquid in the tissues. This method, however,has problems that the uniform dispersion of the liquid in the tissues isdifficult to attain and that the massage may destroy the tissues.Furthermore, such a method, inconveniently, cannot be applied to foodslacking in flexibility.

Also, JP-A-6(1994)/205638 proposes a method for preventing oxidation inproduction of pickles, in which a container containing pickles isdepressurized to pressurize the pickles inside the container by thepressure difference, thereby creating a state where the pickles arebeing pressed by a weight, and simultaneously the oxygen around thepickles is removed to prevent oxidation. This method, which producespickles in a so-called vacuum-packed state, is almost at the same levelin terms of impregnation effects as that using a weight, and needs along time for impregnation with seasonings.

As such, a simple method for impregnating foods with a liquid componentin a short time is strongly demanded.

Moreover, it has been conventional to substitute a gas in a preservativeenvironment for foods, which is air typically, with other gas; forexample, preserving foods in packages filled with nitrogen. It has beenunknown, however, to impregnate foods with a gas by substituting a gasor a liquid in the food tissues with other gas.

Meanwhile, eggs, such as chicken eggs and quail's eggs, are known tocontain well-balanced nutritive components, such as proteins, lipids andminerals, and to be high in nutritional value among other foods. Eggscontain most of essential nutrients for humans except vitamin C.Therefore, the appearance of vitamin C-containing eggs is desired.

Examples of unshelled eggs (eggs with eggshells) known as impregnatedwith nutritive components, seasonings and other components includesmoked eggs, which are prepared by boiling unshelled eggs and smokingthem, and pidans, which are prepared by soaking eggs in a stronglyalkaline paste to denature the proteins in the eggs into a gelled state.Also known are nutritionally enriched eggs produced by chickens or thelike that have been fed with feedstuffs nutritionally enriched by, forexample, iodine and fatty acids.

However, no eggs have been obtained as being enriched in vitamin C, themissing nutrient, and production of vitamin C-containing eggs by feedingchickens or the like with feedstuffs enriched in vitamin C has not beenrealized because, in such cases, the vitamin C in the feedstuffs israrely transferred to the eggs.

It has been concerned, even if the vitamin C is successfully added inthe eggs, that the eggs will have a destroyed flavor due to the strongacid taste of ascorbic acid.

On the other hand, pidans are a traditional Chinese food produced byprocessing duck eggs or the like as ingredients, and are widely knowntoday as a food high in nutritional value and excellent in preservativequality. The pidans generally consist of a brown, gel-like albumenhaving transparency and a dark-green, soft-boiled or hard-boiledconditions of egg yolk, and have a sulfurous or ammonia smell.

The pidans can be prepared by, for example, soaking ingredient eggs in astrongly alkaline liquid containing salt for about 1 to 3 months,coating the resulting eggs with clay or mud and then with hull chaffs,and leaving the eggs at rest for about a half-month to 1 month. It isalso known that the pidans can be prepared by coating ingredient eggsthickly with a clay-like mixture of sodium carbonate, peat mosses, salt,limestone, water, etc, coating the outside of eggs with hull chaffs,placing the eggs in a pot or a can, and leaving the eggs at rest in thesealed pot or can for about 3 to 6 months. It is also known that, inthis production of the pidans, the color of pidans can be controlled byaddition of a tea broth.

As mentioned above, the conventional pidans, although excellent inpreservative quality, need 3 to 6 months, occasionally nearly 1 year forpreparation. Accordingly, producers need to provide a place to store thepidans in preparation at rest over a long period of time.

Also, with the recent development of distribution and refrigeratorstorage technique, foods are required to have a short preparation timerather than excellent preservative quality.

Under these circumstances, there have been demanded a method for readilyimpregnating foods with a liquid component or a gas component in a shorttime, a method for efficiently impregnating eggs with vitamin C or aderivative thereof, and a method for producing pidan-like eggs byefficiently impregnating eggs with an alkali component.

The present inventors made an earnest study in light of suchcircumstances, and found that foods can be favorably impregnated in thetissues thereof with a liquid or a gas in a short period of time byvacuum treating the foods and contacting them with a liquid or a gas, orby cooling the foods in contact with a liquid component. The inventorsalso found that vitamin C-containing eggs and pidan-like eggs can befavorably prepared by the above method. The present invention has beencompleted with such findings.

SUMMARY OF THE INVENTION

The method of impregnation treatment for foods of the present inventioncomprises an impregnation step to impregnate foods with a liquidcomponent or a gas component by contacting the foods with the liquidcomponent or the gas component after a vacuum treatment or in a vacuumstate and/or cooling the foods in contact with the liquid component.

It is also preferable that the impregnation step be a step in which thefoods are vacuum treated, contacted with the liquid component in amaintained vacuum state and then subjected to pressurization, or a stepin which the foods are contacted with the liquid component, vacuumtreated and then subjected to pressurization, or a step in which thefoods are vacuum treated and then subjected to pressurization with theimpregnating gas component.

Preferably, the liquid component or the gas component contains a foodadditive component.

It is also preferable that the pressure in the vacuum treatment or inthe vacuum state range from 10 to 50,000 Pa, that the impregnation stepbe conducted under a temperature condition of −20 to 180° C., and thatthe impregnation step be conducted with the use of a vacuum impregnatingapparatus or a vacuum-pressure impregnating apparatus.

In the method of impregnation treatment for foods of the invention, anultrasonic treatment or a microwave irradiation treatment is preferablyperformed during the impregnation treatment.

The foods are preferably selected from among cereals, meats, fishes,eggs, vegetables, fruits and processed foods. The foods are alsopreferably eggs, more preferably unshelled eggs.

In the method of impregnation treatment for foods, the impregnationstep, when the foods are eggs, is preferably a step in which the eggsare contacted with a liquid component containing vitamin C or aderivative thereof to be impregnated with the vitamin C or thederivative thereof in an amount of 1 to 3,000 mg per 100 g of edible eggportions. In this case, the contact of the eggs with the liquidcomponent containing vitamin C or a derivative thereof is preferablyconducted at −5 to 130° C., more preferably 0 to 55° C. Likewise, it ispreferable that the liquid component contain vitamin C or a derivativethereof and other food-additive component. In the invention, vitaminC-containing eggs can be obtained by the above method.

In the method of impregnation treatment for foods, the impregnationstep, when the foods are unshelled eggs, is preferably a step in whichthe eggs are contacted with a liquid component containing an alkalicomponent to be impregnated in edible portions thereof with the liquidcomponent. In this case, the liquid component preferably has pH of 12 to15, and preferably contains an alkali component and a food additivecomponent other than the alkali component. Also in this case, it ispreferable that the impregnation step be a step in which the eggs areimpregnated with the liquid component in an amount of 1 to 3,000 mg per100 g of edible egg portions. Further in this case, the methodpreferably comprises a heating step to heat the eggs after theimpregnation step. In the invention, pidan-like eggs having atransparent or translucent, gelled albumen can be obtained by the abovemethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a picture of pieces of raw radish, showing the states beforeand after impregnation with a diluted soup base (impregnated pieces onthe left) according to Example 4;

FIG. 2 is a picture of raw eggs (broken state), showing the statesbefore and after impregnation with soy sauce (an impregnated egg on theleft) according to Example 5;

FIG. 3 is a sectional picture of pieces of raw potato used as samples inExample 7 and pieces of raw potato impregnated with soy sauce in Example7 (impregnated pieces on the left);

FIG. 4 is a picture of shelled eggs, one is a treated egg (a) obtainedin Example 20 and the other is an ordinary boiled egg (the treated egg(a) on the left);

FIG. 5 is a picture showing cross sections of shelled and cut eggs, oneis the treated egg (a) obtained in Example 20 and the other is anordinary boiled egg (the treated egg (a) on the left);

FIG. 6 is a picture of shelled eggs, one is a treated egg (b) obtainedin Example 21 and the other is an ordinary boiled egg (the treated egg(b) on the left);

FIG. 7 is a picture showing cross sections of shelled and cut eggs, oneis the treated egg (b) obtained in Example 21 and the other is anordinary boiled egg (the treated egg (b) on the left);

FIG. 8 is a picture of shelled eggs, one is a treated egg (c) obtainedin Example 22 and the other is a likewise heat treated egg (the treatedegg (c) on the left);

FIG. 9 is a picture showing cross sections of shelled and cut eggs, oneis the treated egg (c) obtained in Example 22 and the other is alikewise heat treated egg (the treated egg (c) on the left);

FIG. 10 is a picture of shelled eggs, one is a treated egg (d) obtainedin Example 23 and the other is a likewise heat treated egg (the treatedegg (d) on the left); and

FIG. 11 is a picture showing cross sections of shelled and cut eggs, oneis the treated egg (d) obtained in Example 23 and the other is alikewise heat treated egg (the treated egg (d) on the left).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is illustrated in detail hereinafter.

The method of impregnation treatment for foods of the inventioncomprises an impregnation step of impregnating foods with a liquidcomponent or a gas component.

Various kinds of foods can be subjected to the impregnation treatment ofthe invention without specific limitations. Examples of the foodsemployable in the invention include vegetables, such as leaf vegetables,root vegetables and mushrooms, fruits, cereals, beans, meats, fishes,skins, eggs, eggshells, bones, paste products, processed productsthereof and live stock feed stuffs. Of these, preferably used arecereals, meats, fishes, vegetables, fruits and processed foods. Thesefoods may be raw or have been appropriately cut, crushed, dried, heatedor frozen when subjected to the impregnation treatment.

The above foods generally possess plenty of pores, air gaps or tubulartissues containing moisture, low volatile components or air insidethereof. In the invention, a liquid component or a gas component can beintroduced in the foods by conducting impregnation that physicallysubstitutes the moisture, low volatile components or air existing in thepores, air gaps or tubular tissues of the foods with a liquid componentor a gas component to be introduced.

The method of impregnation treatment for foods of the present inventioncomprises an impregnation step to impregnate the foods with a liquidcomponent or a gas component by contacting the foods with a liquidcomponent or a gas component after a vacuum treatment or in a vacuumstate and/or cooling the foods in contact with a liquid component.

That is, the impregnation step comprises,

a first impregnation step to impregnate the foods with a liquidcomponent by contacting the foods with a liquid component after a vacuumtreatment or in a vacuum state,

a second impregnation step to impregnate the foods with a gas componentby contacting the foods with a gas component after a vacuum treatment orin a vacuum state, or

a third impregnation step to impregnate the foods with a liquidcomponent by cooling the foods in contact with a liquid component.

In the method, these steps are conducted singly or in combination.

Described first is the first impregnation step to impregnate the foodswith a liquid component by contacting the foods with a liquid componentafter a vacuum treatment or in a vacuum state.

In the first and the later-described third impregnation steps toimpregnate the foods with a liquid component, the impregnating liquidcomponent may be any component that can be handled in a liquid state atthe time of impregnation, such as liquids, solutions, slurries anddispersions.

For example, usable as the liquid component are the followingcomponents, which can be according to necessity dispersed or dissolvedin a liquid. These liquid components may be used singly or incombination appropriately.

Examples of the components include liquids, such as water, alcohols,edible oils and chelate liquids; fermented seasonings, such as soy sauceand miso; food extraction components, such as fruit juices and meatjuices; beverages, such as liquors, juices and teas; inorganic salts,such as sodium chloride, potassium chloride, calcium chloride, magnesiumchloride and ferric chloride; alkali components, such as sodiumhydroxide, potassium hydroxide, magnesium hydroxide and ammonia;essential inorganic elements, such as iodine; sweeteners, such assucrose, fructose, glucose, starch syrup, honey, maple syrup and othernatural and artificial sweeteners; acidulants, such as various vinegars,acetic acid, phosphoricacid, lacticacid, malicacid, citricacid, tartaricacid and gluconic acid; bitter components; spices and spice extractioncomponents, such as peppers, red-peppers, mustard, wasabi, garlic andginger; aroma chemicals; oily components; various enzymes andfermentative bacteria; moisturizers, such as glycerol, mirin, caseinsand saccharides; preservatives, such as sorbic acid, benzoates, tanninand polyphenols; germicides, antibacterial agents, bacteriostaticagents; smoke components, such as pyroligneous acid and smoked-foodoils; natural and synthetic pigments, colorants and color fixing agents;dietary fiber components, such as agar-agar and devil's tongue liquids;gelatin components, such as glues and gelatins; antioxidants, such ascatechin and erythorbic acid; nutritional supplements, such as vitaminsand amino acids; medicinal components and medical drugs; qualityimprovers, such as polyphosphates; and other food additive components.

The liquid component employable in the invention should be liquid at thetime of impregnation. That is, ingredients, such as beef tallow, butter,chocolate and the like, which are solid at normal temperature but can behandled as a liquid by adjustment of impregnation conditions, e.g.,temperature, also may be favorably used in the invention.

Of the liquid components mentioned above, particularly preferable arethe liquid components and edible oils containing food additivecomponents, such as seasonings. As mentioned later, liquid componentscontaining vitamin C or a derivative thereof and liquid componentscontaining an alkali component are suitably used when the foods for usein the invention are eggs.

In the first impregnation step, the foods are contacted with the liquidcomponent after a vacuum treatment or in a vacuum state, so that thefoods are impregnated with the liquid component.

To impregnate the foods with the liquid component, any method thatconducts depressurization at least once during the course ofimpregnation of the foods with the liquid component can be employed.Preferably, the foods are contacted with the liquid component eitherafter the vacuum treatment or in a vacuum state. Exemplary preferablemethods of the impregnation include a method (A) in which the foods arevacuum treated (creating a dry vacuum), then contacted with the liquidcomponent in a maintained vacuum state (creating a wet vacuum) andsubjected to pressurization, thereby the foods are impregnated with theliquid component (such a method will be otherwise referred to as the“method (A)”), and a method (B) in which the foods are contacted withthe liquid component, then vacuum treated (creating a wet vacuum) andsubjected to pressurization, thereby the foods are impregnated with theliquid component (such a method will be otherwise referred to as the“method (B)”).

In the first impregnation step, the foods may be contacted with theliquid component after the vacuum treatment, so that the foods areimpregnated with the liquid component. There is no problem in leavingthe vacuum-treated foods in normal pressure before its contact with theliquid component as long as, for example, the vacuum-treated foods arecontacted with the liquid component as immediately as the vacuum statein the foods are maintained.

Described now is the method (A) in which the foods are vacuum treated(creating a dry vacuum), then contacted with the liquid component in amaintained vacuum state (creating a wet vacuum) and subjected topressurization, thereby the foods are impregnated with the liquidcomponent.

In the method (A), the step of vacuum treating the foods, in otherwards, a so-called dry vacuum step of vacuum treating the foods withoutcontact with the impregnating liquid component, the foods are placed ina pressure reducing apparatus and the vicinity of the foods can bedepressurized to usually about 10 to 50,000 Pa, preferably about 100 to10,000 Pa, particularly preferably about 100 to 5,000 Pa. This vacuumtreatment eliminates the moisture, low volatile components or aircontained in the pores, air gaps or tubular tissues of the foods, sothat the pores, air gaps or tubular tissues of the foods are in a stateas much depressurized as the vicinity of the foods. The pressure in thevacuum treatment can be appropriately controlled depending on thetemperature condition and the desired impregnation degree.

In the step of vacuum treating the foods as above, the moisture, lowvolatile components or air contained in the foods are eliminated moreeffectively as the pressure decreases and the vacuum degree increases,so that high-level impregnation can be conducted. However, pressureconditions to enable sufficient elimination of the moisture or the likefrom the foods are different depending on the temperature. The vacuumdegree may be relatively low at high temperatures and tends to need behigh at low temperatures.

Next, the foods, while being kept in a vacuum state, are contacted withthe liquid component. There is no specific limitation on the method ofcontacting the foods with the liquid component as long as the foods canbe sufficiently contacted with the liquid component at portions thereofto be impregnated in a vacuum state. Exemplary methods include soaking.For example, in the case where a container keeping the foods therein isplaced in a pressure reducing apparatus, the contact can be performed byinjecting the liquid component in the container keeping the foodstherein while maintaining the vacuum state created by the vacuumtreatment.

The pressure condition in the vacuum treatment or in the vacuum stateshould be lower than atmospheric pressure. In the vacuum state, thepressure condition is preferably such that the vacuum degree created bythe vacuum treatment is maintained as intact as possible. It is idealthat the pressure in the vacuum state be about 10 to 50,000 Pa,preferably about 100 to 10,000 Pa, particularly preferably about 1,000to 10,000 Pa when the impregnating liquid component is water or asolution, and about 100 to 5,000 Pa when the impregnating liquidcomponent is an oil or an oil solution.

The resulting foods, which have been vacuum treated and contacted withthe liquid component in the maintained vacuum state, are then subjectedto pressurization by pressurizing the pressure reducing apparatus,thereby the foods are impregnated with the liquid component. Thepressurization is ideally conducted such that the surrounding pressureof the foods having been contacted with the liquid component rises tousually about 10,000 Pa to 1.1 MPa, preferably about 0.1 MPa(atmospheric pressure) to 0.9 MPa.

The pressurization can be usually conducted by, for example, releasingthe vacuum state by air purging to raise the pressure to nearlyatmospheric pressure (0.1 MPa), and can be further conducted. To raisethe pressure beyond the atmospheric pressure, a pressurizer can beappropriately employed. For example, such pressurization can beconducted as follows. With the use of a pressure container as acontainer to be subjected to the vacuum treatment, the vacuum treatmentis carried out, and, with the foods soaked in the liquid component, agas such as air, nitrogen gas or carbon dioxide is introduced in theapparatus to raise the pressure to a desired level. In this case,heating can be simultaneously conducted when the pressurization iscarried out by introducing water vapor or alcohol vapor.

The method (A) can favorably substitute, irrespective of whatsoever, aliquid component such as moisture or low volatile components or a gascomponent such as air contained in the pores, air gaps or tubulartissues of the unimpregnated foods with the impregnating liquidcomponent, thereby favorably completing the impregnation treatment.

Described next is the method (B) in which the foods are contacted withthe liquid component, then vacuum treated and subjected topressurization, thereby the foods are impregnated with the liquidcomponent.

In the method (B), performed first is a so-called wet vacuum step ofvacuum treating the unimpregnated foods that have been contacted withthe liquid component by soaking or the like. This step can be carriedout by placing the foods and the liquid component in a container,thereby creating a state in which the foods are soaked in the liquidcomponent, and introducing the container into a pressure reducingapparatus to conduct the vacuum treatment. In the vacuum treatment,ideally, the pressure condition is about 10 to 50,000 Pa, preferablyabout 100 to 10,000 Pa, particularly preferably about 1,000 to 10,000 Pawhen the impregnating liquid component is water or a solution, and about100 to 5,000 Pa when the impregnating liquid component is an oil or anoil solution. In the method (B), as described above, the foods arecontacted with the liquid component in the vacuum state.

The resulting foods, which have been contacted with the liquidcomponent, are then subjected to pressurization by pressurizing thepressure reducing apparatus, thereby the foods are impregnated with theliquid component. The pressurization is ideally conducted, likewise inthe method (A), such that the surrounding pressure of the foods havingbeen soaked in the liquid component rises to usually about 10,000 Pa to1.1 MPa, preferably about 0.1 MPa to 0.9 MPa. The pressurization can beusually conducted by, for example, releasing the vacuum state to raisethe pressure to nearly atmospheric pressure, and can be furtherconducted.

The method (B) is particularly preferable to achieve the impregnation ofthe foods with the liquid component when the unimpregnated foods havepores, air gaps or tubular tissues containing a gas component such asair. The method (B) is particularly preferable to achieve theimpregnation of the foods with the liquid component also when theunimpregnated foods have pores, air gaps or tubular tissues containing aliquid component that has a boiling point lower than that of theimpregnating liquid component.

For example, when fillets of meat or fish, which contain in the tissuesthereof moisture or volatile components of low boiling point, areimpregnated with an aqueous liquid component, such as salt water or soysauce, or an oily component, such as oil or oily seasonings, the vacuumtreatment is conducted to the extent such that the volatile componentsor moisture in the foods are boiled and the impregnating aqueous liquidcomponent or oily component stays unboiled, thereby the volatilecomponents or moisture are eliminated from the foods and the foods arefavorably impregnated with the liquid component by the followingpressurization.

It is particularly preferable that the impregnating liquid component bean oily component, such as oil or oily seasonings, because the state inwhich the moisture in the foods is boiled and the impregnating oilycomponent remains unboiled can be readily created. Such a state can bereadily created by adjusting vacuum conditions even when the foods arefrozen foods or the like that require the impregnation treatment to beconducted at low temperatures, for example, temperatures lower thannormal temperature. For example, when the impregnation treatment isperformed in a state in which the moisture-containing foods are soakedin oil, it is observed that the moisture in the foods alone is boiled tocreate a tempura-cooking state, showing that the foods are favorablyimpregnated with the oil component.

In the above first impregnation step, the foods can be impregnated withthe above-mentioned various kinds of components as a liquid component,so that flavoring, improvement of flavor and eating texture,sterilization and addition of medicinal components, nutritivecomponents, colorants and other various additives can be attained.

Described next is the second impregnation step to impregnate the foodswith a gas component by contacting the foods with a gas component afterthe vacuum treatment or in the vacuum state. In the second impregnationstep, the foods are contacted with a gas component after the vacuumtreatment or in the vacuum state to be impregnated with the gascomponent.

Examples of the gas component with which the foods are impregnatedinclude gases obtained by evaporating a liquid, such as water vapor,alcohol vapor and volatile material vapor; gases containing aromachemicals or other various additives; and other gases, such as oxygen,carbon dioxide, ethylene, nitrogen, noble gases and air. These gases canbe used either individually or in combination appropriately.

Preferably, the contact of the foods with the gas component after thevacuum treatment or in the vacuum state is made in a pressure reducingapparatus containing the foods having been vacuum treated or in thevacuum state. Also preferably, the impregnating gas component isintroduced in the pressure reducing apparatus. To introduce theimpregnating gas component into the pressure reducing apparatus, forexample, the gas can be directly introduced into the pressure reducingapparatus after the vacuum treatment, or a liquid can be introduced intothe pressure reducing apparatus after the vacuum treatment andthereafter can be vaporized, or the foods and a liquid are placed in thepressure reducing apparatus without contact and the liquid can bevaporized by the vacuum treatment.

By these methods described above, the foods and the impregnating gascomponent can be favorably contacted with each other after the vacuumtreatment or in the vacuum state. When a liquid is vaporized by thevacuum treatment to produce air and the foods are contacted with the airto be impregnated therewith, the liquid may have been appropriatelyheated.

To attain impregnation of the foods with the gas component in the secondimpregnation step, any method that conducts depressurization at leastonce during the course of impregnation of the foods with the gascomponent can be employed. Ideally, the foods are first vacuum treatedand then subjected to pressurization with the impregnating gas componentto be impregnated with the gas component.

In the method (B), likewise in the first impregnation step of the method(A), the step of vacuum treating the foods is conducted such that thefoods are placed in a pressure reducing apparatus and the vicinity ofthe foods is depressurized to usually about 10 to 50,000 Pa, preferablyabout 100 to 10,000 Pa, particularly preferably about 100 to 5,000 Pa.In this case, the pressure reducing apparatus has been preferably purgedwith the impregnating gas component. This vacuum treatment eliminatesthe moisture, low volatile components or air contained in the pores, airgaps or tubular tissues of the foods, so that the pores, air gaps ortubular tissues of the foods are in a state as much depressurized as thevicinity of the foods. The pressure in the vacuum treatment can beappropriately controlled depending on the desired impregnation degree orthe like. It is mentioned that the moisture, low volatile components orair contained in the foods are eliminated more effectively as thepressure decreases and the vacuum degree increases, so that high-levelimpregnation can be conducted.

Subsequently, the vicinity of the vacuum-treated foods is pressurizedwith the impregnating gas component, thereby the foods are impregnatedwith the gas component. The pressurization is ideally conducted suchthat the pressure reducing apparatus, in which the foods and the gascomponent have been contacted with each other, is pressurized with thegas component to a pressure condition of usually about 100 Pa to 2 MPa,preferably about 10,000 Pa to 1.1 MPa, particularly preferably about 0.1to 0.9 MPa. The pressurization can be made by pressurizing the pressurereducing apparatus with the impregnating gas component to nearlyatmospheric pressure, and can be further conducted.

The above method to impregnate the foods with the gas component can beused for various purposes, such as promoting fermentation of kimchi andpickles by impregnating them with enzyme, avoiding food-qualitydeterioration, such as oxidation, by impregnating the foods with aninert gas, such as nitrogen, controlling germination and promoting agingby introducing an ethylene gas, and substituting air inside the foodswith a gas.

The method of impregnation treatment for foods of the invention thatenables impregnating the foods with the liquid component or the gascomponent, may comprise a treatment to vibrate the foods, such asultrasonic treatment, which is conducted during the impregnationtreatment. The vibrating treatment, such as ultrasonic treatment, can beperformed continuously over all the steps in the impregnation treatment,or in some of the steps. To conduct such a treatment in a stage of thevacuum treatment is preferable because the moisture, low volatilecomponents or air contained in the foods can be more smoothlyeliminated. It is also preferable to conduct the vibrating treatment,such as ultrasonic treatment, in a stage of the pressurization becausethe foods can be more smoothly impregnated with the liquid component orthe gas component.

Described next is the third impregnation step to impregnate the foodswith the liquid component by cooling the foods in contact with theliquid component.

The liquid component to impregnate the foods with in the thirdimpregnation step can be, likewise in the first impregnation step, anycomponent that can be handled in a liquid state at the time ofimpregnation, such as liquids, solutions, slurries and dispersions.Examples of the liquid component include the same ones as described withrespect to the first impregnation step.

The following are exemplary preferable methods to impregnate the foodswith the liquid component by cooling the foods in contact with theliquid component.

1. The foods, in a state of being soaked in the liquid component, arecooled by 5° C. or more, preferably 10° C. or more, thereby the foodsare impregnated with the liquid component.

2. The foods are soaked in the liquid component, heated and, as beingsoaked in the liquid component, cooled to normal temperature or below,thereby the foods are impregnated with the liquid component.

3. The heated foods are soaked in the liquid component of a temperaturelower than that of the foods to be cooled in contact with the liquidcomponent, thereby the foods are impregnated with the liquid component.

In the third impregnation step, it is preferable that the temperaturedifference in the cooling be made large by heating and cooling of thefoods at best temperatures within the limits preventing unintendeddenaturation of the foods. In such a case, the impregnation of the foodswith the liquid component can be performed more preferably.

The third impregnation step, which can be applied to every kind offoods, is particularly effective when the foods have integuments on thesurface, such as eggs with eggshells. For example, when eggs witheggshells are cooled in contact with the liquid component, the yolks,albumens and air-space gases in the eggshells are heat-shrunk by thetemperature difference in the cooling but the eggshells itself arehardly heat-shrunk, thereby a vacuum state is created in the eggshells.Accordingly, it is presumed that the liquid component in contact withthe eggshells impregnates inside the eggshells through the eggshellpores, thereby the eggs are favorably impregnated with the liquidcomponent. It is therefore preferable that the temperature difference inthe cooling be large. Ideally, the foods are cooled by usually 5° C. ormore, preferably 10° C. or more, still preferably 20° C. or more. Asmentioned in the above examples, heating prior to the cooling ispreferable. When the eggs are heated as unshelled, the yolks, albumensand air-space gases in the eggshells are heat-swollen, so that the airand, occasionally, portion of the moisture contained inside theeggshells are discharged outside the eggshells. When such eggs arecooled in contact with the liquid component, components inside theeggshells are shrunk by a larger degree to enable efficientlyimpregnating the eggs with the liquid component.

In the third impregnation step with the cooling mentioned above, it ispreferable to conduct pressurization after the cooling to impregnate thefoods further effectively with the liquid component.

In the invention, the above impregnation steps can be carried out incombination appropriately.

It is needless to say that the liquid component or the gas componentused in these impregnation steps may contain food-additive componentsother than those specified above.

There is no specific limitation on the temperature conditions in theimpregnation steps of the present invention. The impregnation steps canbe appropriately carried out under desired temperature conditionsaccording to the types of the foods and the liquid component, and,ideally, are conducted at usually −20 to 180° C., preferably −10 to 150°C., particularly preferably −5 to 120° C.

When the impregnation step is a step of contacting the foods with theliquid component or the gas component after the vacuum treatment or inthe vacuum state (the first and the second impregnation steps), theimpregnation can be preferably attained with the use of a vacuumimpregnating apparatus or a vacuum-pressure impregnating apparatus.Particularly, it is more preferable to perform the impregnation by theuse of a vacuum-pressure impregnating apparatus because operationthereof is simple and, even if the pressurization is conducted byapplication of pressure, the treatment can be carried out smoothly.

In the method of impregnation treatment for foods of the invention, theimpregnation treatment is preferably accompanied by heating, heatinsulation or cooling, or a microwave irradiation treatment can beperformed. The microwave irradiation treatment may be performed for thepurpose of, for example, defrosting the frozen foods, heat insulation byavoiding lowering of temperature owning to removal of latent heat whenthe moisture is vaporized under vacuum, cooking, or sterilization. Themicrowave irradiation treatment can be performed continuously over allthe steps in the impregnation treatment, or in some of the steps.

Also, in the method of impregnation treatment for foods according to theinvention, stirring can be conducted during the impregnation treatment.Stirring during the impregnation treatment is preferable because theimpregnation treatment can be effected more evenly. The stirring duringthe impregnation treatment is performed for the purpose of, for example,impregnating the foods evenly with the liquid component or the gascomponent, or, under vacuum conditions, evenly discharging the liquidcomponent or the gas component contained in the foods from the piledfoods. The stirring can be performed continuously over all the steps inthe impregnation treatment, or in some of the steps.

In the method of impregnation treatment for foods of the invention, thefoods may be pre-treated before the impregnation treatment. Examples ofthe pre-treatment include any treatments applicable to foods, such ascutting, freezing, defrosting, heating, drying, flavoring, stirring,pressurizing, depressurizing and drug-treating. In carrying out thepresent invention, it is preferable in view of good impregnationefficiency that the frozen foods be semi-defrosted or defrosted for use.

In the method of impregnation treatment for foods of the invention, anafter-treatment may be performed for the foods after the impregnationtreatment. Examples of the after-treatment include any treatmentsapplicable to foods, such as cutting, freezing, defrosting, heating,drying, flavoring, stirring, pressurizing, depressurizing anddrug-treating. Otherwise, the after-treatment may be a treatment thatremoves extra components of the impregnating components. For example,extra liquid components can be removed from the foods impregnated withthe liquid component by drying or a dehydration treatment.

In the method of impregnation treatment for foods of the invention, theimpregnation degree can be adjusted by controlling treatment conditions,such as vacuum degree or cooling degree, thereby the foods can beimpregnated at a desired impregnation degree. For example, it ispossible to produce the foods that have been impregnated evenly into thecenter part and the foods that have been impregnated only at the surfacearea. Specifically, when eggshells are to be sterilized and foodsurfaces to be colored, the foods can be impregnated only at the surfacearea by controlling the vacuum degree in the vacuum treatment.

According to the method of impregnation treatment for foods of theinvention, the foods can be impregnated with the liquid component or thegas component in a very short period of time. Further, when theimpregnation step is conducted such that the foods are contacted withthe liquid component or the gas component after the vacuum treatment orin the vacuum state, the impregnation treatment can be performed atnormal temperature without heating or cooling. Accordingly, even if thefoods to be impregnated are perishable foods or the like, the foods canbe impregnated without deteriorating its eating texture.

By the method of impregnation treatment for foods of the invention,various kinds of foods can be readily impregnated with various kinds ofliquid components or gas components.

Moreover, the method of impregnation treatment for foods allows forobtaining vitamin C-containing eggs, which has never been realized.Described below is the method of impregnation treatment for foods toimpregnate eggs with vitamin C or a derivative thereof (otherwisereferred to as the method for preparing vitamin C-containing eggshereinafter).

In the invention, eggs are contacted with a liquid component containingvitamin C or a derivative thereof (these will be otherwise referred toas the vitamin C component hereinafter), so that the eggs areimpregnated with the vitamin C component in an amount of 1 to 3,000 mg,preferably 1 to 2,500 mg per 100 g of edible egg portions, therebyvitamin C-containing eggs are prepared.

Examples of the eggs preferably used in production of the vitaminC-containing eggs include chicken eggs, duck eggs and quail's eggs. Theeggs may be unshelled eggs or heat-treated shelled eggs, ideallyunshelled eggs. When the eggs are unshelled eggs, they may be raw orboiled. Particularly preferably, the eggs are unshelled raw eggs.

Examples of the vitamin C-component with which the eggs are impregnatedinclude vitamin C (L-ascorbic acid) and derivatives thereof, such asascorbic acid metallic salts. Particularly preferably, the vitaminC-component is sodium ascorbate. The liquid component used in the methodfor preparing vitamin C-containing eggs contains at least one vitamin Ccomponent selected from the above examples.

Examples of the liquid component containing the vitamin C componentinclude liquid components prepared by dissolving or dispersing thevitamin C component in an edible liquid, such as water, alcohols,alcohol-containing water, edible oils, seasoning liquids, liquors andchelate liquids. Preferably, the liquid component is an aqueous solutioncontaining at least one of the vitamin C components dissolved therein.

Ideally, the liquid component containing the vitamin C component has aconcentration of the vitamin C component, which is not particularlylimited thereto, of usually about 1 to 50% by weight, preferably about 5to 30% by weight.

The liquid component containing the vitamin C component may furthercontain a food additive component other than vitamin C or the vitamin Cderivative. That is, the liquid component containing the vitamin Ccomponent preferably used herein may be one prepared by dissolving ordispersing the vitamin C component in any of the liquid componentsexemplified as the liquid components with which the foods areimpregnated in the first and the third impregnation steps.

Of the food additive components, the inorganic metallic elements may beused as salts of L-ascorbic acid. Such seasonings as L-glutamic acid,glycine, inosinic acid and sorbitol have an effect of inhibitingoxidation decomposition of the L-ascorbic acid, and therefore preferablyused in combination with the vitamin C component.

In the method of preparing vitamin C-containing eggs of the invention,the eggs are contacted with the above-described liquid componentcontaining the vitamin C component, thereby the eggs are impregnatedwith the vitamin C component. The contact of the eggs and the liquidcomponent containing the vitamin C component can be made by such amethod as, for example, soaking the eggs in the liquid component orspraying the liquid component on the eggs. The eggs are preferablysoaked in the liquid component for contact because, in that way, theentire egg surface can be evenly contacted with the liquid component.Also, the contact of the eggs and the liquid component containing thevitamin C component may be conducted after the vacuum treatment of theeggs or in the vacuum state, and under normal pressure or underpressure.

To impregnate the eggs with the vitamin C component, any of the firstimpregnation step and the third impregnation step mentioned above toimpregnate the foods with the liquid component can be employed. That is,the impregnation step may be conducted in a manner such that the eggsare contacted with the liquid component containing the vitamin Ccomponent after the vacuum treatment or in the vacuum state, or in amanner such that the eggs are cooled in contact with the liquidcomponent containing the vitamin C component.

Specifically, the above impregnation step in which the eggs arecontacted with the liquid component containing the vitamin C componentafter the vacuum treatment or in the vacuum state is, for example, astep in which the eggs are vacuum treated and, in the maintained vacuumstate, contacted with the liquid component containing the vitamin Ccomponent and thereafter subjected to pressurization, or a step in whichthe eggs are contacted with the liquid component containing the vitaminC component, vacuum treated and thereafter subjected to pressurization.Specific operations in the above impregnation steps are as describedabove.

In the method for preparing vitamin C-containing eggs by theimpregnation step with the vacuum treatment, gases in air spaces of theeggs are substituted with the liquid component, so that the impregnatedeggs sometimes gain weight. In such a case, the air volume in theeggshells has been reduced. Accordingly, when the resulting vitaminC-containing eggs are raw and heated to give boiled eggs, it is frequentthat the edible portions and the eggshells have a high sticking degree,which results in difficult shelling of the eggs. Therefore, in themethod of preparing vitamin C-containing eggs, in which the eggs arecontacted with the liquid component containing the vitamin C componentafter the vacuum treatment or in the vacuum state to be impregnatedtherewith, the eggs may be subjected to another vacuum treatment afterthe impregnation step in order to control a substantial increase of theegg weight.

In the above method of preparing vitamin C-containing eggs, in which theeggs are contacted with the liquid component containing the vitamin Ccomponent after the vacuum treatment or in the vacuum state to beimpregnated therewith, the impregnation degree with the vitamin Ccomponent can be adjusted by controlling the vacuum degree or the like,thereby the eggs can be impregnated with a desired vitamin C content.Particularly, when the ingredients are boiled eggs, it is possible toproduce the eggs that have been impregnated with vitamin C only in thealbumens by controlling the vacuum degree in the vacuum treatment.

The following are exemplary preferable impregnation steps of cooling theeggs in contact with the liquid component containing the vitamin Ccomponent.

1. The raw or boiled eggs are soaked in the liquid component containingthe vitamin C component and, in that state, cooled by 5° C. or more,preferably 10° C. or more, thereby the vitamin C-containing raw eggs areobtained.

2. The raw eggs are soaked in the liquid component containing thevitamin C component, heated to 75° C. or over to be boiled in the liquidcomponent and, as being soaked in the liquid component, cooled to normaltemperature or below, thereby the vitamin C-containing boiled eggs areobtained.

3. The raw eggs are brought into a boiled egg state by heating to 75° C.or over in water or steam and then cooled to normal temperature or belowby soaking in the liquid component containing the vitamin C component,thereby the vitamin C-containing boiled eggs are obtained.

4. The raw eggs are soaked in the liquid component containing thevitamin C component, heated to 55° C. or below, preferably from 45 to55° C. and then cooled to normal temperature or below, preferably from 0to 10° C., thereby the vitamin C-containing raw eggs are obtained.

5. The raw eggs are heated to 55° C. or below, preferably from 45 to 55°C. in water or steam and soaked in the liquid component containing thevitamin C component to be cooled to normal temperature or below,preferably from 0 to 10° C., thereby the vitamin C-containing raw eggsare obtained.

When the unshelled eggs are cooled in contact with the liquid componentcontaining vitamin C or the vitamin C derivative, the yolks, albumensand air-space gases in the eggshells are heat-shrunk by the temperaturedifference in the cooling but the eggshells itself are hardlyheat-shrunk, so that a vacuum state is created in the eggshells.Accordingly, it is presumed that the liquid component containing thevitamin C component that is in contact with the eggshells impregnatesinside the eggshells through the eggshell pores, thereby the eggs arefavorably impregnated with the vitamin C component. It is thereforepreferable that the temperature difference in the cooling be large.Ideally, the foods are cooled by usually 5° C. or more, preferably 10°C. or more, still preferably 20° C. or more.

As mentioned in the above examples, heating prior to the cooling ispreferable. When the eggs are heated as unshelled, the yolks, albumensand air-space gases in the eggshells are heat-swollen, so that the airand, occasionally, portion of the moisture contained inside theeggshells are discharged outside the eggshells. When such eggs arecooled in contact with the liquid component containing the vitamin Ccomponent, components inside the eggshells are shrunk by a larger degreeto enable efficiently impregnating the eggs with the vitamin Ccomponent.

In the method of preparing vitamin C-containing eggs with cooling, it ispreferable to conduct pressurization after the cooling because the eggscan be further effectively impregnated with the vitamin C component.

Production of the vitamin C-containing eggs with cooling can be carriedout in combination with the above vacuum treatment.

There is no specific limitation on the temperature conditions in theimpregnation step to impregnate the eggs with the liquid componentcontaining the vitamin C component. The temperature in the impregnationstep is usually about −5 to 130° C. Particularly, when the eggs are rawbefore the impregnation and are to be produced into the raw vitaminC-containing eggs, the impregnation step is conducted under thetemperature condition of 0 to 55° C.

In the case of preparing the vitamin C-containing eggs as well, theimpregnation treatment may be accompanied by a vibrating treatment, suchas ultrasonic treatment, heating, heat insulation, cooling or amicrowave irradiation treatment. These treatments may be performedcontinuously over all the steps in the impregnation treatment, or insome steps. It is preferable to conduct the ultrasonic treatment duringthe course of impregnation treatment because the eggs can be moresmoothly impregnated with the vitamin C-containing liquid component. Themicrowave irradiation treatment may be conducted for the purpose of, forexample, warming the raw eggs in a raw state, heat insulation byavoiding lowering of temperature owning to removal of latent heat whenthe moisture is vaporized under vacuum, cooking, or sterilization.

In the method of preparing vitamin C-containing eggs, the eggs can beimpregnated with the liquid component that contains, in addition to thevitamin C component, various kinds of food additive components, so thatnot only impregnation with the vitamin C component but also flavoring,improvement of flavor and eating texture, sterilization and addition ofmedicinal components, nutritive components, colorants and other variousadditives can be attained.

According to the above method, the eggs can be impregnated with thevitamin C-containing liquid component in a very short period of time.Further, the impregnation treatment can be performed at normaltemperature without heating or cooling, so that the raw eggs can beimpregnated without losing a raw state.

The vitamin C-containing eggs of the invention are the eggs obtained bythe above method of impregnation treatment for foods (the method ofpreparing vitamin C-containing eggs) These eggs contain vitamin C(L-ascorbic acid) or the derivative thereof in an amount of 1 to 3,000mg, preferably 1 to 2,500 mg per 100 g of edible egg portions (excludingthe eggshells).

The vitamin C-containing eggs obtained in the invention satisfactorilycontain the vitamin C component usually in both the edible yolk portionand the edible albumen portion. Also, when the impregnating vitamin Ccomponent is an ascorbic acid metallic salt, such as sodium ascorbate,the resulting vitamin C-containing eggs do not taste acid and have thesame flavor and the same look as those of ordinary eggs. Therefore, theeggs can be used the same as ordinary eggs.

The above method of impregnation treatment for foods enablesimpregnating the unshelled eggs with the liquid component containing analkali component, so that pidan-like eggs in which at least albumens aregelled like jellies and the albumens have transparency can be obtained.Described below is the method of impregnation treatment for foodscomprising an impregnation step, in which the eggs are contacted with aliquid component containing an alkali component and thereby the edibleegg portions are impregnated with the liquid component (otherwisereferred to as the method of preparing pidan-like eggs hereinafter).

The pidan-like eggs dealt with in this specification are eggs in whichat least albumens are gelled like jellies and the albumens havetransparency. The albumens having transparency used in the specificationcomprehend all albumens having any transparency at all in comparisonwith albumens of ordinary boiled eggs that are completely whitened. Thatis, the albumens may be colorless and transparent or translucent ones,or colored and transparent or translucent ones.

The ingredient eggs for the method of preparing pidan-like eggs areselected from duck eggs, quail's eggs and chicken eggs, which arepreferably unshelled.

Also, the ingredient eggs may be unheated eggs or heated eggs that havebeen heated to the extent of avoiding completion of gelation ofalbumens. In other words, the eggs preferably used in the method ofpreparing pidan-like eggs are the eggs in which the gelation of albumenshas not been completed, such as the eggs in which the albumens are notgelled at all, or the eggs in which the albumens are incompletely gelled(e.g., so-called hot spring eggs). The eggs in which the albumens arecompletely gelled by heating, such as boiled eggs, are not preferable asthe ingredient eggs for the method of preparing pidan-like eggs.

The liquid component containing an alkali component that is contactedwith the eggs can be any type as long as containing an alkali component.However, it is ideal that the liquid component have a high pH value,such as 12 to 15, preferably 12.5 to 15, more preferably 13.5 to 14.5.

Examples of the alkali component that can be contained in the liquidcomponent include sodium hydroxide, potassium hydroxide, aqueousammonia, sodium phosphate, potassium phosphate and sodium carbonate.Examples of the liquid component include those prepared by dissolving ordispersing any of the above alkali components in an edible liquid, suchas water, alcohol-containing water, edible oils, seasoning liquids,liquors and chelate liquids. Preferably, the liquid component is anaqueous solution containing at least one of the alkali componentsdissolved therein.

It is also preferable that the liquid component containing the alkalicomponent further contain a food additive component other than thealkali component. Examples of the food additive component other than thealkali component include the same ones as exemplified above to becontained in the liquid components of the first and the thirdimpregnation steps. When the food additive component is a liquid, theliquid may be used as a base of the liquid component.

It is preferable in the method of preparing pidan-like eggs that theliquid component contain salt or a coloring component, such as a blacktea extraction component, as the food additive component other than thealkali component. It is preferable that the liquid component containsalt and the coloring component in addition to the alkali componentbecause, in such a case, obtained are the pidan-like eggs that aresimilar to ordinary pidans in appearance, eating texture and flavor.

In the method of preparing pidan-like eggs, the eggs can be impregnatedwith the liquid component that contains, in addition to the alkalicomponent, various kinds of food additive components, so that not onlyimpregnation with the alkali component but also flavoring, improvementof flavor and eating texture, sterilization and addition of medicinalcomponents, nutritive components, colorants and other various additivescan be attained. It is sanitary to conduct the impregnation step becausethe liquid component containing the alkali component can effectsterilization on the egg surfaces.

The method of preparing pidan-like eggs comprises the impregnation stepto impregnate the edible egg portions with the liquid componentcontaining the alkali component by contacting the eggs with the liquidcomponent.

To impregnate the eggs with the alkali component, any of the firstimpregnation step and the third impregnation step to impregnate thefoods with the liquid component can be employed. Specifically, theimpregnation step may be conducted such that the eggs are contacted withthe liquid component containing the alkali component after the vacuumtreatment or in the vacuum state, or such that the eggs are cooled incontact with the liquid component containing the alkali component.

Specifically, the above impregnation step of contacting the eggs withthe liquid component containing the alkali component after the vacuumtreatment or in the vacuum state is, for example, a step in which theeggs are vacuum treated and, in the maintained vacuum state, contactedwith the liquid component containing the alkali component and thereaftersubjected to pressurization, or a step in which the eggs are contactedwith the liquid component containing the alkali component, vacuumtreated and thereafter subjected to pressurization. Specific operationsin the above impregnation steps are as described above.

The following are exemplary preferable impregnation steps ofimpregnating the eggs with the liquid component containing the alkalicomponent by cooling the eggs in contact with the liquid component.

1. The raw eggs or the eggs that have been heated to the extent ofavoiding completion of gelation of albumens are cooled by 5° C. or more,preferably 10° C. or more by soaking in the liquid component containingthe alkali component to be impregnated in edible portions thereof withthe liquid component, thereby the pidan-like eggs are prepared.

2. The raw eggs are soaked in the liquid component containing the alkalicomponent, heated to the extent of avoiding completion of gelation ofalbumens and, as being soaked in the liquid component, cooled to beimpregnated in edible portions thereof with the liquid component,thereby the pidan-like eggs are prepared. Preferably, the cooling isenough to cool the eggs to normal temperature or below.

In the impregnation step to impregnate the unshelled eggs with theliquid component containing the alkali component with cooling, thetemperature difference in the cooling is preferably large for the samereason as in the above-noted case where the unshelled eggs are cooled incontact with the liquid component containing the vitamin C component.Ideally, the eggs are cooled by usually 5° C. or more, preferably 10° C.or more, still preferably 20° C. or more. It is also preferable to heatthe eggs before the cooling. In the method of preparing pidan-like eggswith such a cooling method, it is preferable to perform pressurizationfor the eggs after the cooling because the eggs can be more effectivelyimpregnated with the liquid component.

In the above impregnation step in the method of preparing pidan-likeeggs, the impregnation degree with the alkali component can be adjustedby controlling the vacuum degree, the cooling degree or the like,thereby the eggs can be impregnated with a desired alkali-componentcontent. The ideal amount of the liquid component in which the eggs areimpregnated with in the impregnation step, although variable dependingon the alkali-component concentration in the liquid component, is about1 to 3,000 mg, preferably about 500 to 3,000 mg, more preferably about500 to 2,500 mg per 100 g of edible egg portions. In the invention, thepidan-like eggs can be prepared with desired albumen transparency bycontrolling the alkali-component concentration in the liquid componentused in the impregnation step, the amount of the impregnating liquidcomponent or the like.

The method of preparing pidan-like eggs that comprises the aboveimpregnation step allows for impregnating the eggs with the liquidcomponent containing the alkali component in a very short period oftime. Particularly, in the method comprising the impregnation step withthe vacuum treatment, the impregnation treatment can be performed atnormal temperature without heating or cooling, so that the raw eggs canbe impregnated without losing a raw state after the impregnationtreatment.

In the above impregnation steps, gases in air spaces of the eggs aresubstituted with the liquid component, so that the impregnated eggssometimes gain weight. In such a case, the air volume in the eggshellshas been reduced. Accordingly, when the eggs are heated after theimpregnation step, it is frequent that the edible portions and theeggshells have an increased sticking degree, which results in difficultshelling of the eggs. Therefore, the eggs may be subjected to anothervacuum treatment after the impregnation step in order to control asubstantial increase of the egg weight.

The liquid component containing the alkali component that has remainedafter the impregnation step may be reused in another impregnation stepfor the untreated eggs.

In the case of preparing the pidan-like eggs as well, the impregnationtreatment may be accompanied by a vibrating treatment, such asultrasonic treatment, heating, heat insulation, cooling or a microwaveirradiation treatment. These treatments may be performed in all thesteps in the impregnation treatment, or in some steps.

It is preferable to conduct the ultrasonic treatment during the courseof impregnation treatment because the eggs can be more smoothlyimpregnated with the alkali-component containing liquid component. Thealkali component that has impregnated in the eggs reacts with theproteins in the eggs and neutralizes the amino acid, so that, after theimpregnation step, the edible egg portions can have pH within the ediblerange. The microwave irradiation treatment may be conducted for thepurpose of, for example, warming the raw eggs in a raw state, heatinsulation by avoiding lowering of temperature owning to removal oflatent heat when the moisture is vaporized under vacuum, cooking, orsterilization. The microwave irradiation treatment may be performedcontinuously over all the steps in the impregnation treatment, or insome steps. When the microwave irradiation treatment is conducted forthe purpose of cooking, the treatment is ideally conducted after theimpregnation is partially completed, more preferably in the latter halfor after completion of the impregnation step.

In the method of preparing pidan-like eggs, production of the pidan-likeeggs can be satisfactorily achieved even by leaving at rest the eggsthat have been subjected to the above impregnation step because theproteins in the albumens are denatured by the alkali to form atransparent or translucent gel. However, production of the pidan-likeeggs in which the albumens are a transparent or translucent gel can bemade in a more reduced time by conducting a heat treatment.

Examples of the heat treatment include, likewise in making ordinaryboiled eggs, soaking the eggs in a high-temperature liquid, such as hotwater, after the impregnation step, irradiating the eggs with amicrowave after the impregnation step, and steaming the eggs after theimpregnation step. The heat treatment is conducted under conditions suchthat the albumens are gelled, or, ideally, such that the albumens aregelled and the yolks are soft boiled or hard boiled conditions asdesired.

When the heat treatment is conducted by such a method as soaking theeggs in a high-temperature liquid, such as hot water, after theimpregnation step, the high-temperature liquid may contain a foodadditive component other than the alkali component, so that the eggs canbe impregnated with more food additive components.

According to the method of preparing pidan-like eggs, the pidan-likeeggs in which the albumens are a transparent or translucent and,according to necessity, colored gel can be prepared readily and in ashort period of time with good productivity. Also, according to thepresent invention, the pidan-like eggs in which the albumens havedesired transparency, and the pidan-like eggs having a desired flavorand a desired color can be prepared.

The pidan-like eggs of the invention are obtained by the above method ofpreparing pidan-like eggs, and have albumens that are a transparent ortranslucent gel.

The pidan-like eggs of the invention in which the gelation of albumenshas been completed can be impregnated, in a shelled state, with variouscomponents by being soaked in the liquid component containing thevarious components or by being well boiled in the liquid.

The pidan-like eggs obtained in the invention can be readily eatenwithout a treatment with mud, clay or lime components, which has been aproblem with ordinary pidans. Moreover, the pidan-like eggs of theinvention generate less waste products.

EXAMPLES

The present invention will be further illustrated with reference to thefollowing examples, which is not to limit the scopes of the invention inany way.

Example 1

A lean meat portion of frozen tuna was cut into a piece of 100 mm×100mm×15 mm to make a sample. The sample weight was 86.800 g. The samplewas placed in a 300-ml beaker, and the beaker was set in an ultrasoniccleaning vessel. Then, the ultrasonic cleaning vessel was placed in avacuum-pressure impregnating tank (produced by PLACERAM CO., LTD.).Subsequently, a vacuum (dry vacuum) was drawn to depressurize thevacuum-pressure impregnating tank to 2,000 Pa, and the vacuum drawingwas continuously carried out for another 10 minutes. As a result, thepressure reached 100 Pa.

Then, the vacuum drawing was temporarily stopped, and rapeseed oil(NISSHIN CANOLA OIL, produced by THE NISSHIN OIL MILLS, LTD.) was pouredin the beaker until the sample was completely soaked in the oil, and theultrasonic cleaning vessel was operated at 25 W and 40 kHz. The pressureat this time had risen to about 1,000 Pa. Thereafter, the vacuum (wetvacuum) drawing was performed for 10 minutes, thereby the pressurereached 100 Pa. During the wet vacuum drawing, a large number of bubbleswere confirmed to generate from the sample, which was the evidence thatthe moisture in the sample was being substituted with the impregnatingoil.

After the vacuum drawing was terminated, the vacuum-pressureimpregnating tank was purged with air and thereafter pressurized byintroduction of compressed air. The tank was maintained at 0.8 MPainside for 10 minutes and thereafter purged with air.

The sample was taken out of the tank and the beaker. The oil sitting onthe sample surface was removed by a scraper, thereby lean tuna meatimpregnated with rapeseed oil (A) was obtained. The lean tuna meatimpregnated with rapeseed oil (A) was in a defrosted state and weighed88.870 g. That is, the weight increase by 2.070 g (2.4%) was confirmedin comparison with the sample weight before the treatment.

The obtained lean tuna meat impregnated with rapeseed oil (A) was cutinto bite-size pieces. Then, 13 panelists were asked to try and evaluatethe lean tuna meat on the five items, which were appearance, flavor,eating texture, taste and total, based on the following criteria. Thetotal point of all the items was collected from each of the panelists.The results of the evaluation based on the sum total point by thepanelists (13 members) and the results of the evaluation of theuntreated lean tuna meat (defrosted state) are shown in Table 1.

(Evaluation Criteria)

Very good: +5 points

Rather good: +3 points

Good and bad: 0 point

Rather bad: −3 points

Very bad: −5 points

Example 2

Lean tuna meat impregnated with rapeseed oil (B) was obtained in thesame manner as in Example 1, except that a lean meat portion ofdefrosted tuna (86.115 g), which had been defrosted from a frozen stateat normal temperature, was used as a sample in place of the lean meatportion of frozen tuna. The obtained lean tuna meat impregnated withrapeseed oil (B) weighed 89.850 g, and the weight increase by 3.735 g(4.3%) was confirmed in comparison with the sample weight before thetreatment. The lean tuna meat impregnated with rapeseed oil (B) wasevaluated in the same manner as in Example 1. The results are shown inTable 1.

TABLE 1 Example 1: Example 2: Lean tuna meat Lean tuna meat impregnatedimpregnated with rapeseed with rapeseed Untreated lean oil (A) oil (B)tuna meat Evaluation 33 62 13 Result (sum total point) Evaluation 2 1 3Ranking

As a result of the evaluation by tasting, the lean tuna meatsimpregnated with rapeseed oil obtained in Examples 1 and 2 wereevaluated by many panelists that they were less dry and crumby, hadresistance to the teeth and a favorable eating texture in comparisonwith the untreated lean tuna meat.

With these results, it was confirmed that the lean tuna meatsimpregnated with rapeseed oil obtained in Examples 1 and 2 had a uniformappearance on the cut surface and had been favorably impregnated withrapeseed oil. Also, the lean tuna meats impregnated with rapeseed oilobtained in Examples 1 and 2 had been improved in flavor in comparisonwith the untreated lean tuna meat and were thus suitable for eating.

Further, the results of Example 1 and Example 2 proved that any of thefrozen and defrosted foods can be satisfactorily impregnated with theliquid component and that the defrosted foods can have a higherimpregnation degree than that of the frozen foods when treated under thesame conditions.

Example 3

A poly net was laid on a bottom of a 4-litter glass beaker, and,thereon, raw beef that weighed 204.369 g (a round-meat block, 60 mm×60mm×60 mm, refrigerated at 6° C.) was placed. Then, the glass beaker wasset in the same vacuum-pressure impregnating tank as used in Example 1.

Subsequently, the vacuum (dry vacuum) drawing was carried out todepressurize the vacuum-pressure impregnating tank to 850 Pa, and thevacuum drawing was continuously carried out for another 10 minutes. As aresult, it was confirmed that a liquid had oozed on the surface of thesample raw beef. Next, milk (condensed type, MEIRAN ASPER MILK) waspoured in the beaker until the sample raw beef was completely soaked inthe milk, and the vacuum (wet vacuum) drawing was further conducted for10 minutes.

After the vacuum drawing was terminated, the vacuum-pressureimpregnating tank was purged with air and thereafter pressurized byintroduction of compressed air. The tank was maintained at 0.6 MPainside for 10 minutes and thereafter purged with air.

The sample was taken out of the beaker, and the milk sitting on thesample surface was removed by a scraper, thereby raw beef impregnatedwith milk was obtained. The obtained raw beef impregnated with milkweighed 209.266 g. That is, the weight increase by 4.897 g (2.4%) wasconfirmed in comparison with the sample weight before the treatment. Theobtained raw beef impregnated with milk had been changed in color due tothe overall impregnation with milk. With that, it was confirmed that theimpregnation had been favorably effected deeply into the inside.

Example 4

Raw radish was peeled by a thickness of about 1 mm and cut into roundslices and fan-shaped pieces, thereby samples were prepared with shapesshown in Table 2. A poly net was laid on a bottom of a 4-litter glassbeaker, and, thereon, the samples were placed. Then, the glass beakerwas set in the same vacuum-pressure impregnating tank as used in Example1.

Subsequently, the vacuum (dry vacuum) drawing was performed todepressurize the vacuum-pressure impregnating tank to 1,000 Pa, and thevacuum drawing was continuously carried out for another 10 minutes.Then, a kimchi-flavored light-pickling base liquid (produced by EBARAFOODS INDUSTRY CO., INC.) or a diluted soup base, which had beenprepared by diluting a soup base (the one for boil-cooking, produced byMITSUKAN CO,. LTD.) with water in the proportion of 1:5 (soupbase:water), was poured in the beaker until the samples were completelysoaked therein. Then, the vacuum (wet vacuum) drawing was performed for10 minutes. The kimchi-flavored light-pickling base liquid was comprisedof a seasoning solution containing ground red-peppers and the likesuspended therein.

Next, the vacuum-pressure impregnating tank was purged with air andthereafter pressurized by introduction of compressed air. The tank wasmaintained at 0.6 MPa inside for 10 minutes and thereafter purged withair.

The samples were taken out of the beaker, and the light-pickling baseliquid or the diluted soup base sitting on the sample surfaces wasremoved by a scraper, thereby impregnated raw radish samples wereobtained. The results of weight measurement thereof are shown in Table2. Also, the states before and after the impregnation with the dilutedsoup base are shown in a picture of FIG. 1.

TABLE 2 Shape of Weight Weight raw before after Weight Weight radishImpregnating impregnation impregnation change change sample liquid type(g) (g) (g) rate (%) Round Light-pickling 186.352 178.533 −7.799 −4.19slice base liquid Fan Light-pickling 204.804 194.311 −10.493 −5.12 shapebase liquid Round Diluted 187.555 186.724 −0.831 −0.44 slice soup baseFan Diluted 192.225 192.023 −0.202 −0.11 shape soup base

In this Example, although the weight decrease was observed after theimpregnation, it was well confirmed that all the samples had beenimpregnated with the light-pickling base liquid or the diluted soup basealmost evenly into the inside.

Example 5

Raw eggs (chicken eggs with white eggshell), whose weight are shown inTable 3, were used as samples. The samples were placed in a 2000-mlglass beaker, and, thereon as a weight, a metal net was laid. The beakerwas set in the same vacuum-pressure impregnating tank as used in Example1.

Subsequently, the vacuum (dry vacuum) drawing was performed todepressurize the vacuum-pressure impregnating tank to 1,300 Pa, and thevacuum drawing was further carried out for another 10 minutes.

Then, soy sauce (undiluted, Kikkoman Soy Sauce produced by KIKKOMANCORPORATION) was poured in the beaker until the samples were completelysoaked therein, and the vacuum (wet vacuum) drawing was furtherconducted for 10 minutes.

Next, the vacuum-pressure impregnating tank was purged with air andthereafter pressurized by introduction of compressed air. The tank wasmaintained at 0.6 MPa inside for 10 minutes and thereafter purged withair.

The samples were taken out of the beaker and were lightly washed withwater to remove the soy sauce sitting on the sample surfaces, therebyraw eggs impregnated with soy sauce were obtained. The obtained raw eggsimpregnated with soy sauce had a light coffee color on the eggshellsurface due to the effect of the impregnation with soy sauce. Breakingof the eggs revealed that they had the same light coffee color on theinner side of eggshell as well. Also, as shown in FIG. 2, the raw eggsitself (albumens and yolks) resulting from the breaking had took on abrown color in comparison with eggs unimpregnated with soy sauce. Whentasted, these eggs had a soy sauce flavor. With that, it was confirmedthat the eggs had been impregnated with soy sauce into the inside. Theresults of weight measurement thereof are shown in Table 3.

TABLE 3 Weight Weight Weight before after Weight change Sampleimpregnation impregnation change rate raw egg (g) (g) (g) (%) 1 66.52367.565 1.042 1.566 2 68.370 69.379 1.009 1.476 3 64.877 65.829 0.9521.467

When the obtained raw eggs impregnated with soy sauce were boiled, theresulting boiled eggs had taken on a coffee color in the albumens andhad a soy sauce flavor.

Example 6

The impregnation treatment with soy sauce was conducted in the samemanner as in Example 5, except that the boiled eggs prepared under thecondition of a boiling time of 10 minutes were used in place of the raweggs, thereby boiled eggs impregnated with soy sauce were obtained.

The obtained boiled eggs impregnated with soy sauce had a light coffeecolor on the eggshell surface due to the effect of the impregnation withsoy sauce. Breaking and cutting of the eggs revealed that the albumensalso had the same light coffee color and the yolks had a weak browncolor. When tasted, these eggs had a soy sauce flavor. With that, it wasconfirmed that the eggs had been impregnated with soy sauce into theinside.

Example 7

The impregnation treatment with soy sauce was conducted in the samemanner as in Example 5, except that peeled raw potato was used as asample in place of the raw eggs, thereby raw potato impregnated with soysauce was obtained.

The obtained raw potato impregnated with soy sauce had taken on a coffeecolor on the surface due to the effect of the impregnation with soysauce. When the potato was cut and observed, the whole section had acoffee color, as shown in FIG. 3. With that, it was confirmed that thepotato had been almost evenly impregnated with soy sauce into the centerpart. When tasted, the potato was confirmed to have a soy sauce flavoreven in the inside.

Further, the raw potato impregnated with soy sauce was cooked by heatingin a microwave oven at 500 W for 2 minutes, thereby cooked potatoimpregnated with soy sauce was obtained. Tasting of the cooked potatorevealed that the potato had a uniform soy sauce flavor in every part.

Example 8

An unshelled white raw egg was used as a sample. The sample was placedin a vacuum-pressure impregnating tank (produced by PLACERAM CO., LTD.)at normal temperature. Subsequently, the vacuum (dry vacuum) drawing wasperformed to depressurize the vacuum-pressure impregnating tank to 700Pa, and the vacuum drawing was continuously carried out for another 10minutes. As a result, the pressure reached 100 Pa.

Then, the vacuum drawing was temporarily stopped, and a 9-wt % sodiumascorbate aqueous solution was poured in the tank until the sample wascompletely soaked therein. The pressure in the tank at this time was 700Pa or below. Then, compressed air was introduced in the tank with thesample in a soaked state, and the tank was maintained at 4.9×10⁵ Pa(0.49 MPa) inside for 10 minutes. Thereafter, the aqueous solution wasdischarged from the tank by applying a low pressure with air. The tankwas then purged with air, thereby a vitamin C-containing egg (a1) wasobtained.

When the obtained vitamin C-containing egg (a1) was broken, the insidestate visually observed was the same as that of an ordinary raw egg. Theamount of total vitamin C (ascorbic acid and derivatives thereof) in theedible portions (all egg portions except the eggshell) of the vitaminC-containing egg (a1) was 140 mg/100 g. The total vitamin C content (thesum of vitamin C and derivatives thereof) was determined by a highperformance liquid chromatography.

Example 9

Vitamin C-containing eggs (a2) and (a3) obtained in the same manner asin Example 8 were soaked in water and then heated. After maintained inboiling for 10 minutes, the eggs were cooled, thereby vitaminC-containing boiled eggs were obtained.

The obtained vitamin C-containing boiled egg (a2) had a total vitamin Ccontent in the edible egg portions of 104 mg/100 g, and the vitaminC-containing boiled egg (a3) had a total vitamin C content in the entireegg portions including the eggshell of 98 mg/100 g.

Example 10

A vitamin C-containing egg (a4) obtained in the same manner as inExample 8 was heated on a fluorine-coated frying pan until both the yolkand the albumen were hardened, thereby a fried egg was prepared. Theobtained vitamin C-containing fried egg (a4) had a total vitamin Ccontent of 107 mg/100 g.

Example 11

A vitamin C-containing egg (b1) was obtained in the same manner as inExample 8, except that a 29-wt % sodium ascorbate aqueous solution wasused as the sodium ascorbate aqueous solution.

When the obtained vitamin C-containing egg (b1) was broken, the insidestate visually observed was the same as that of an ordinary raw egg. Theamount of total vitamin C in the edible portions (all egg portionsexcept the eggshell) of the vitamin C-containing egg (b1) was 433 mg/100g.

Example 12

Vitamin C-containing eggs (b2), (b3) and (b4) obtained in the samemanner as in Example 11 were soaked in water and heated. Aftermaintained in boiling for 10 minutes, the eggs were cooled, therebyvitamin C-containing boiled eggs were obtained.

The obtained vitamin C-containing boiled egg (b2) had a total vitamin Ccontent in the edible egg portions of 396 mg/100 g, the vitaminC-containing boiled egg (b3) had a total vitamin C content in the yolkof 117 mg/100 g and that in the albumen of 433 mg/100 g, and the vitaminC-containing boiled egg (b4) had a total vitamin C content in the entireegg portions including the eggshell of 272 mg/100 g.

Example 13

A vitamin C-containing egg (b5) obtained in the same manner as inExample 11 was heated on a fluorine-coated frying pan until both theyolk and the albumen were hardened, thereby a fried egg was prepared.The obtained vitamin C-containing fried egg (b5) had a total vitamin Ccontent of 432 mg/100 g.

Example 14

A vitamin C-containing boiled egg (c1) was obtained in the same manneras in Example 11, except that a boiled egg (unshelled), which had beenprepared by heating a white egg in water, maintaining it in boiling for10 minutes and then cooling it to 5° C., was used in place of the whiteraw egg.

The amount of total vitamin C in the edible portions (all egg portionsexcept the eggshell) of the vitamin C-containing boiled egg (c1) was 743mg/100 g.

Example 15

An unshelled white raw egg (62.60 g; the weight inclusive of theeggshell) was used as a sample. The sample was placed in avacuum-pressure impregnating tank (produced by PLACERAM CO., LTD.) atordinary temperature. Subsequently, the vacuum (dry vacuum) drawing wasperformed to depressurize the vacuum-pressure impregnating tank to 700Pa, and the vacuum drawing was continuously carried out for another 10minutes. As a result, the pressure reached 100 Pa. The egg weight atthis time was 62.31 g (the weight inclusive of the eggshell), which hadchanged in relation to the egg weight before the treatment by a weightchange rate −0.47%.

Then, the vacuum drawing was temporarily stopped, and a 29-wt % sodiumascorbate aqueous solution was poured in the tank until the sample wascompletely soaked therein. The pressure in the tank at this time was 700Pa or below. The tank was then purged with air to create an atmosphericpressure state in the tank. The egg weight at this time was 62.9 g,which had changed in relation to the egg weight before the treatment bya weight change rate of +0.47%.

Then, compressed air was introduced in the tank with the sample in asoaked state, and the tank was maintained at 4.9×10⁵ Pa inside for 10minutes. The egg weight at this time was 63.3 g, which had changed inrelation to the egg weight before the treatment by a weight change rateof +1.06%.

Thereafter, the aqueous solution was discharged from the tank byapplying a low pressure with air. The vacuum-pressure impregnating tankwas then depressurized again to 700 Pa, and the vacuum drawing wascontinuously carried out for another 30 minutes. The vacuum drawing wasthen terminated, and the vacuum-pressure impregnating tank was purgedwith air, thereby a vitamin C-containing egg (d1) was obtained. The eggweight of the obtained vitamin C-containing egg (d1) was 62.5 g (theweight inclusive of the eggshell). The weight change rate in relation tothe egg weight before the treatment was −0.11%, which is to say that theweight was almost the same before and after the treatment.

When the obtained vitamin C-containing egg (d1) was broken, the insidestate visually observed was the same as that of an ordinary raw egg. Theamount of total vitamin C in the edible portions (all egg portionsexcept the eggshell) of the vitamin C-containing egg (d1) was 184 mg/100g.

Example 16

A vitamin C-containing egg prepared in the same manner as in Example 15was heated in water, maintained in boiling for 10 minutes and thencooled, thereby a vitamin C-containing boiled egg (d2) was obtained.

The obtained vitamin C-containing boiled egg (d2) had a yolk and analbumen completely hardened. The vitamin C-containing boiled egg (d2)had a total vitamin C content in the yolk of 109 mg/100 g and that inthe albumen of 249 mg/100 g.

Example 17

A white raw egg was soaked in a 29-wt % sodium ascorbate aqueoussolution of ordinary temperature, heated therein and maintained inboiling for 10 minutes. Thereafter, the egg was cooled to 5° C. in astate of being soaked in the sodium ascorbate aqueous solution, therebya vitamin C-containing boiled egg (e) was obtained. The obtained vitaminC-containing boiled egg (e) had a yolk and an albumen completelyhardened. The vitamin C-containing boiled egg (e) had a total vitamin Ccontent in the yolk of 368 mg/100 g and that in the albumen of 1,200mg/100 g.

Example 18

A white raw egg was soaked in water and heated therein to 50° C. The eggwas then soaked in a 29-wt % sodium ascorbate aqueous solution of 5° C.for cooling and maintained therein for 10 minutes, thereby a vitaminC-containing egg (f) was obtained.

When the obtained vitamin C-containing egg (f) was broken, the insidestate visually observed was the same as that of an ordinary raw egg. Theamount of total vitamin C in the edible portions (all egg portionsexcept the eggshell) of the vitamin C-containing egg (f) was 329 mg/100g.

Example 19

A white raw egg was soaked in a 29-wt % sodium ascorbate aqueoussolution of ordinary temperature, heated therein to 50° C. andmaintained for 10 minutes. Thereafter, the egg was cooled to 5° C. in astate of being soaked in the sodium ascorbate aqueous solution andmaintained for 10 minutes, thereby a vitamin C-containing egg (g) wasobtained.

When the obtained vitamin C-containing egg (g) was broken, the insidestate visually observed was the same as that of an ordinary raw egg. Theamount of total vitamin C in the edible portions (all egg portionsexcept the eggshell) of the vitamin C-containing egg (g) was 268 mg/100g.

Example 20

An unshelled white raw chicken egg was used as a sample. The sample wasplaced in a vacuum-pressure impregnating tank (produced by PLACERAM CO.,LTD.) at ordinary temperature. Subsequently, a vacuum (dry vacuum) wasdrawn to depressurize the vacuum-pressure impregnating tank to 700 Pa,and the vacuum drawing was continuously carried out for another 10minutes. As a result, the pressure reached 100 Pa.

Then, the vacuum drawing was temporarily stopped, and a 4-wt % sodiumhydroxide aqueous solution (pH: 14.0) was poured in the tank until thesample was completely soaked therein. The pressure in the tank at thistime was 700 Pa or below. Then, compressed air was introduced in thetank with the sample in a soaked state, and the tank was maintained at4.9×10⁵ Pa (0.49 MPa) inside for 10 minutes. Thereafter, the aqueoussolution was discharged from the tank by applying a low pressure withair, thereby an egg impregnated with the sodium hydroxide aqueoussolution was obtained.

The egg impregnated with the sodium hydroxide aqueous solution wassoaked in water and heated therein. After maintained in boiling for 15minutes, the egg was cooled with water, thereby a treated egg (a) wasobtained. The treated egg (a) had an eggshell surface which had not beenchanged in color tone and which remained white.

The treated egg (a) was then shelled. The resulting appearance wascompared with that of an ordinary boiled egg prepared by heat treatingan untreated egg, which had not been impregnated with an alkalisolution, in the same manner as with the egg impregnated with the sodiumhydroxide aqueous solution.

The treated egg (a) thus obtained was gelled just like an ordinaryboiled egg, and had a transparent albumen to show the inside yolktherethrough. With that, it was confirmed that a favorable pidan-likeegg had been prepared.

FIG. 4 is a picture showing the shelled states of the treated egg (a)and an ordinary boiled egg. FIG. 5 is a picture showing the crosssections of the treated egg (a) and an ordinary boiled egg.

Example 21

A heat-treated egg (b) impregnated with aqueous ammonia was obtained inthe same manner as in Example 20, except that a 15% ammonia aqueoussolution (pH: 13.6) was used in place of the 4-wt % sodium hydroxideaqueous solution. The treated egg (b) had an eggshell surface which hadnot been changed in color tone and which remained white.

The treated egg (b) was then shelled. The resulting appearance wascompared with that of an ordinary boiled egg prepared by heat treatingan untreated egg, which had not been impregnated with an alkalisolution, in the same manner as with the egg impregnated with the sodiumhydroxide aqueous solution.

The treated egg (b) thus obtained was gelled just like an ordinaryboiled egg, and had a translucent albumen to show the inside yolktherethrough. With that, it was confirmed that a favorable pidan-likeegg had been prepared.

FIG. 6 is a picture showing the shelled states of the treated egg (b)and an ordinary boiled egg. FIG. 7 is a picture showing the crosssections of the treated egg (b) and an ordinary boiled egg.

Example 22

An unshelled white raw chicken egg was used as a sample. The sample wassoaked in hot water kept at 59° C. and maintained therein for 40 minutesfor heating. When an egg that had been treated in the same manner aswith the sample egg was observed for the egg state at this time, it wasfound that the egg was a so-called hot spring egg in which portion ofthe albumen was incompletely gelled.

Subsequently, the heated sample egg was soaked in a 15% sodium hydroxideaqueous solution (pH: 14.5) kept at 10° C. and left at rest therein for5 hours, thereby an egg impregnated with the sodium hydroxide aqueoussolution was obtained.

The obtained egg impregnated with the sodium hydroxide aqueous solutionwas then soaked in water of ordinary temperature, gradually heated to90° C., maintained at 90° C. for 20 minutes and cooled with water,thereby a treated egg (c) was obtained. The treated egg (c) had aneggshell surface which had not been changed in color tone and whichremained white.

The treated egg (c) was then shelled. The resulting appearance wascompared with that of an egg obtained by heat treating an untreated egg,which had not been impregnated with an alkali solution, in the samemanner as with the egg impregnated with the sodium hydroxide aqueoussolution.

The treated egg (c) thus obtained was gelled just like an ordinaryboiled egg, and had a translucent albumen to show the inside yolktherethrough. With that, it was confirmed that a favorable pidan-likeegg had been prepared.

FIG. 8 is a picture showing the shelled states of the treated egg (c)and an ordinary boiled egg. FIG. 9 is a picture showing the crosssections of the treated egg (c) and an ordinary boiled egg.

Example 23

An unshelled white raw chicken egg of ordinary temperature was used as asample. The sample was soaked in a 15% sodium hydroxide aqueous solution(pH: 14.5) of ordinary temperature, cooled to 4° C. and left at resttherein at 4° C. for 18 hours, thereby an egg impregnated with thesodium hydroxide aqueous solution was obtained.

The obtained egg impregnated with the sodium hydroxide aqueous solutionwas then soaked in water of ordinary temperature, gradually heated to90° C., maintained at 90° C. for 20 minutes and cooled with water,thereby a treated egg (d) was obtained. The treated egg (d) had aneggshell surface which had not been changed in color tone and whichremained white.

The treated egg (d) was then shelled. The resulting appearance wascompared with that of an egg obtained by heat treating an untreated egg,which had not been impregnated with an alkali solution, in the samemanner as with the egg impregnated with the sodium hydroxide aqueoussolution.

The treated egg (d) thus obtained was gelled just like an ordinaryboiled egg, and had a translucent albumen to show the inside yolktherethrough. With that, it was confirmed that a favorable pidan-likeegg had been prepared.

FIG. 10 is a picture showing the shelled states of the treated egg (d)and an ordinary boiled egg. FIG. 11 is a picture showing the crosssections of the treated egg (d) and an ordinary boiled egg.

1. A method of impregnation treatment for foods comprising the steps ofimpregnating a food with one of a liquid component or a gas component bycontacting the food with the liquid component or the gas component afterone of a vacuum treatment or in a vacuum state, wherein an irradiationtreatment is performed during the impregnation treatment.
 2. A method ofimpregnation treatment for foods comprising the steps of impregnating afood with one of a liquid component or a gas component by contacting thefood with the liquid component or the gas component after one of avacuum treatment or in a vacuum state, wherein a microwave irradiationtreatment is performed during the impregnation treatment.
 3. A method ofimpregnation treatment for foods comprising the steps of impregnating afood with a liquid component by contacting the food with the liquidcomponent after one of a vacuum treatment or in a vacuum state, whereinthe food is unshelled egg and the impregnation step is a step in whichthe egg is contacted with a liquid component containing an alkalicomponent to be impregnated in edible portions thereof with the liquidcomponent.
 4. The method of impregnation treatment for foods as claimedin claim 3, wherein the liquid component has pH of 12 to
 15. 5. Themethod of impregnation treatment for foods as claimed in claim 3,wherein the liquid component contains an alkali component and a foodadditive component other than the alkali component.
 6. The method ofimpregnation treatment for foods as claimed in claim 3, wherein theimpregnation step is a step in which the eggs are impregnated with theliquid component in an amount of 1 to 3,000 mg per 1000 g of edible eggportions.
 7. The method of impregnation treatment for foods as claimedin claim 3, further comprising a heating step to heat the eggs after theimpregnation step.
 8. A pidan-like egg that has a transparent ortranslucent, gelled albumen, said pidan-like egg obtained by the methodof impregnation treatment for foods as claimed in claim
 3. 9. A methodof impregnation treatment for foods comprising the steps of impregnatinga food with one of a liquid component or a gas component by contactingthe food with the liquid component or the gas component after one of avacuum treatment or in a vacuum state and cooling the food in contactwith the liquid component, wherein an irradiation treatment is performedduring the impregnation treatment.
 10. A method of impregnationtreatment for foods comprising the steps of impregnating a food with oneof a liquid component or a gas component by contacting the food with theliquid component or the gas component after one of a vacuum treatment orin a vacuum state and cooling the food in contact with the liquidcomponent, wherein a microwave irradiation treatment is performed duringthe impregnation treatment.
 11. A method of impregnation treatment forfoods comprising the steps of impregnating a food with a liquidcomponent by contacting the food with the liquid component after one ofa vacuum treatment or in a vacuum state and cooling the food in contactwith the liquid component, wherein the food is unshelled egg and theimpregnation step is a step in which the egg is contacted with a liquidcomponent containing an alkali component to be impregnated in edibleportions thereof with the liquid component.
 12. The method ofimpregnation treatment for foods as claimed in claim 11, wherein theliquid component has pH of 12 to
 15. 13. The method of impregnationtreatment for foods as claimed in claim 11, wherein the liquid componentcontains an alkali component and a food additive component other thanthe alkali component.
 14. The method of impregnation treatment for foodsas claimed in claim 11, wherein the impregnation step is a step in whichthe eggs are impregnated with the liquid component in an amount of 1 to3,000 mg per 1000 g of edible egg portions.
 15. The method ofimpregnation treatment for foods as claimed in claim 11, furthercomprising a heating step to heat the eggs after the impregnation step.16. A pidan-like egg that has a transparent or translucent, gelledalbumen, said pidan-like egg obtained by the method of impregnationtreatment for foods as claimed in claim 11.